1. Field of the Invention
The present invention relates to an electric-component transferring apparatus, a method of taking respective images of electric components (i.e., circuit components as elements of an electric or electronic circuit), and a system for mounting electric components on a circuit substrate such as a printed circuit board.
2. Related Art Statement
There is known an electric-component ("EC") transferring device which includes an EC holder for holding an EC, a shaft member for supporting the EC holder, and a moving device for moving the EC holder in a direction intersecting an axis line of the shaft member, and thereby transferring the EC in that direction. This sort of EC transferring device is disclosed in, e.g., Japanese Patent Application laid open for public inspection under No. 8(1996)-78882. The disclosed device includes an EC holder which holds an EC; a shaft member whose lower end portion supports the EC holder; a movable member having a support hole which supports the shaft member such that the shaft member is rotatable about an axis line relative to the movable member and is movable relative to the movable member in an axial direction parallel to the axis line; and a moving device which moves the movable member in a direction intersecting the axis line of the shaft member.
The above-indicated EC transferring device is employed as an EC mounting device which takes an EC from an EC supplying device and mounts the EC on a printed circuit board ("PCB") as a sort of circuit substrate that is an object on which ECs are to be mounted. The EC mounting device includes an EC mounting head; an X-Y robot which moves the EC mounting head in each of two directions perpendicular to each other on a horizontal plane; a Z-axis/.theta.-axis motor which is provided on the X-Y robot, which moves the head in a vertical direction (i.e., a Z-axis direction) perpendicular to the horizontal plane, and which rotates the head about a vertical axis line; and an EC-image taking device which is provided between the EC supplying device and the PCB.
The Z-axis/.theta.-axis motor includes a Z-axis motor portion and a .theta.-axis motor portion which are integrated with each other and each of which includes an AC servomotor (i.e., brushless DC servomotor). The Z-axis motor portion further includes a nut which is supported by an upper portion of a housing such that the nut is rotatable about a vertical axis line and is not movable in an axial direction parallel to the axis line; and a ball screw which is fitted in the housing such that the ball screw is movable in an axial direction thereof, and is not rotatable, relative to the housing and which is screwed with the nut. A permanent magnet which is fixed to an outer circumferential surface of the nut provides a rotor of the AC servomotor of the Z-axis motor portion. The rotor is opposed to a stator core which is provided in the housing. The stator core includes a plurality of coils. An electric current which is supplied to the coils is so controlled as to rotate the nut by an arbitrary angle in each of opposite directions and thereby move the ball screw over an arbitrary distance in each of upward and downward directions.
A lower portion of the housing supports a ball-spline member which is concentric with the ball screw and which is rotatable, and is not movable in an axial direction thereof, relative to the housing. A spline-axis member is fitted in the ball-spline member such that the spline-axis member is not rotatable, and is movable in an axial direction thereof, relative to the ball-spline member. A permanent magnet which is fixed to the ball-spline member provides a rotor of the AC servomotor of the .theta.-axis motor portion. The rotor is opposed to another stator core which is provided in the housing. The second stator core includes a plurality of second coils. An electric current which is supplied to the second coils is so controlled as to rotate the ball-spline member by an arbitrary angle in each of opposite directions and thereby move the spline-axis member over an arbitrary angle in a corresponding one of the opposite directions.
The spline-axis member is connected to the ball screw such that the spline-axis member is rotatable, and not movable in its axial direction, relative to the ball screw. The EC mounting head is attached to a lower end portion of the spline-axis member. The spline-axis member and the ball screw cooperate with each other to provide a shaft member whose lower end portion supports an EC holder, and respective inner holes of the nut and the ball-spline member cooperate with each other to define a support hole which supports the shaft member. When the ball screw is moved up and down, the spline-axis member is moved up and down and the EC mounting head is moved up and down. When the spline axis member is rotated, the head is rotated about its axis line. While the head is moved down and then up, the head takes an EC from the EC supplying device, or mounts the EC on the PCB. While the head is rotated, a possible angular error of the EC held by the head from a reference angular position about a vertical axis line may be corrected. Since the EC mounting head is moved up and down, and rotated, by the single Z-axis/.theta.-axis motor including the upper Z-axis motor portion and the lower .theta.-axis motor portion integrated with each other, the EC mounting device enjoys a simple construction as compared with one in which a Z-axis motor and a .theta.-axis motor are employed as separate members.
However, the two servomotors are used, one for moving the EC mounting head up and down, and the other for rotating the head. In addition, the ball screw and the spline-axis member are connected to each other such that they are rotatable, and not movable in their axial direction, relative to each other. Thus, the EC mounting device suffers from a high production cost. Moreover, since the nut, the ball-spline member, the rotors, and the stators are provided around the ball screw and the spline-axis member, the EC mounting device suffers from a large size.
Japanese Patent Application laid open for public inspection under Publication No. 7(1995)-45995 discloses an EC mounting system including an EC sucker which sucks and holds an EC by applying vacuum thereto, and an EC supplying device which supplies an EC to the EC sucker. Thus, the EC sucker takes the EC from the EC supplying device, and subsequently mounts the EC on a CS. However, the EC held by the EC sucker may have an positional error from a reference position on a plane intersecting an axis line of the EC sucker. This positional error is an error of the center of the EC relative to the axis line of the EC sucker, and results from the dislocation of the EC on the EC supplying device, from its reference position relative to the supplying device, and/or the misalignment of the EC relative to the EC sucker when the EC is sucked by the sucker. To solve this problem, it has been practiced to employ an EC-image taking device which takes an image of the EC taken by the EC sucker from the EC supplying device and calculate, based on the taken image, a positional error of the EC held by the sucker from its reference position relative to the sucker. This positional error is corrected before the EC is mounted on the CS, and accordingly the EC is accurately mounted at a prescribed EC-mount place on the CS.
In the above-indicated EC mounting system, the EC sucker is supported by a movable member which is movable in each of an X-axis and a Y-axis direction which are perpendicular to each other on a horizontal plane, and the EC-image taking device is provided between the EC supplying device and a CS supporting device which supports the CS. While the EC sucker is moved toward the CS supporting device after taking the EC from the EC supplying device, the EC-image taking device takes an image of the EC held by the EC sucker.
In the above EC mounting system, the movable member supports the single EC sucker. Therefore, each time one EC is mounted on the CS, the movable member goes and backs between the EC supplying device and the CS supporting device. If the movable member would support a plurality of EC suckers, a plurality of ECs could be mounted on the CS while the movable member goes and backs one time between the EC supplying device and the CS supporting device. This would lead to improving the efficiency of mounting of ECs.
However, the EC-image taking device can take, at one time, an image of only one EC. Therefore, each time an image of one EC is taken, the movable member must be moved to position the next EC at an image-take position. This operation needs a long time, which leads to lowering the efficiency of mounting of ECs.